Nov. 26  Global warming could level out in the 22nd century, say scientists who have
for the first time pushed their computer models of the world's climate to 2200.

Previous models had shown that efforts to cut greenhouse gas emissions would
only slightly slow the Earth's warming by the year 2100, but had not looked
further out, said Aiguo Dai of the National Center for Atmospheric Research in Boulder, Colo.

Dai's study on the future of Earth's climate appears in the Dec. 1 issue
of Geophysical Review Letters.

"The thing I think is striking is that you see a lot more effect from
controlling carbon dioxide (a greenhouse gas) over the next hundred years
(from 2099 to 2199)," said Robert Dickinson, a climate modeler at the
Georgia Institute of Technology.

And while that's good news, it can only
happen if people start reducing greenhouse gas emissions today, he pointed
out.

"You're talking about long-time scales," said Dickinson. "This is part
of the problem of getting political will (to make changes today)."

Dai's computer-powered peephole into the 21st and 22nd centuries also
provided some cautionary news. When the model was run with the assumption
that nothing is done to control current greenhouse gas emissions 
conditions he calls Business As Usual  global temperatures continue to rise
unabated.

In both scenarios, the areas hardest hit by rising temperatures are at high
latitudes. And while some people might not consider warmer weather in
Alaska, for instance, to be a problem, said Dickinson, the melting of
permafrost under buildings, the flood of rainwater into dams that that once
fell as snow and the rise in sea level could pose major problems worldwide.

There are several reasons that climate modelers have not previously looked beyond
the year 2100, said Dai. One reason is that it takes an awful lot of
computer power to run a model into another century. There's also a lot less confidence in the results from a model that ventures too far into the
unknown, said Dai.

One of the few areas that's understood well enough to
risk such long-range study is global temperature, he said. Climate models
can also predict changes in rainfall, winds and storm tracks, but these are
less certain when extended beyond 2100, he said.

The take-home message, said Dai, is that there are clear benefits for
reducing greenhouse emissions today, for which our great-great-great
grandchildren no doubt will be grateful.